1. Field of the Invention
The present invention relates to a voice communications apparatus, and more particularly, to a voice communications apparatus built in, or accommodating, a telephone set and also to a voice communications system including the same.
2. Description of the Background Art
Today, VoIP (Voice over Internet Protocol), i.e. voice communications using Internet or similar IP (Internet Protocol) network is spreading. Even for voice communications using an IP network, it is necessary to transmit voice signals limited in frequency band up to 4 kHz, i.e. so-called telephone-band signals. This is because voice signals higher than 4 kHz are inhibited from being input to a wired transmission path or general public switched telephone network. By contrast, an IP network is free from such a limitation and can implement voice communications using a broad band, i.e. signals lying in a frequency band above 4 kHz.
More specifically, as shown in FIG. 2, a conventional telephone set, as distinguished from an IP telephone set exclusively connectable to an IP network, has a transmitter characteristic that limits a broad-band signal input to its microphone to 4 kHz or below. As also shown in FIG. 2, the receiver characteristic of the conventional telephone set limits a signal received over its transmission path to 4 kHz or below before the signal is output from its earphone or loudspeaker. As a result, even when the transmission path allows signals above 4 kHz to be transmitted like with an IP network, voice quality achievable is not higher than when the transmission path is a general public switched telephone network. The transmitter and receiver characteristics stated above are implemented by band-pass filters by way of example.
In the above circumstances, high-quality communications using broad-band signals are not attainable with an IP network unless a telephone set itself is provided with a transmitter and a receiver characteristic adaptive to a broad band. However, with many of conventional telephone sets, it is impossible to enjoy high voice quality particular to an IP network or similar transmission path, which allow broad-band signals, due to the transmitter and receiver characteristics that limit the frequency band to 4 kHz or below, as stated above.